Infectious Diseases Practice Questions

Q: Mites are known to transmit which of the following diseases?

Scabies. **Explanation:** **Correct Option: A. Scabies** Scabies is a contagious skin infestation caused by the itch mite, ***Sarcoptes scabiei* var. *hominis***. The female mite burrows into the stratum corneum of the skin to deposit eggs, leading to a delayed type IV hypersensitivity reaction. This results in the characteristic intense nocturnal pruritus and polymorphic lesions (vesicles, pustules, and burrows). **Analysis of Incorrect Options:** * **B. Relapsing Fever:** Louse-borne relapsing fever is transmitted by the **Body Louse** (*Pediculus humanus corporis*), while tick-borne relapsing fever is transmitted by **Soft Ticks** (*Ornithodoros*). * **C. Kyasanur Forest Disease (KFD):** This viral hemorrhagic fever is transmitted to humans via the bite of infected **Hard Ticks** (*Haemaphysalis spinigera*). * **D. Human Babesiosis:** This malaria-like parasitic disease is transmitted by the bite of **Hard Ticks** (specifically *Ixodes scapularis*). **High-Yield Clinical Pearls for NEET-PG:** * **Mite-borne diseases:** Apart from Scabies, mites are vectors for **Scrub Typhus** (transmitted by the *Leptotrombidium* chigger mite) and **Rickettsialpox** (*Liponyssoid sanguineus*). * **Scabies Treatment:** The drug of choice is **Permethrin 5% cream** (applied neck down overnight). Oral **Ivermectin** (200 µg/kg) is an alternative, especially for crusted (Norwegian) scabies. * **Vector Distinction:** Always distinguish between **Mites** (Scabies, Scrub Typhus) and **Ticks** (KFD, Babesiosis, Indian Tick Typhus) as they are frequently confused in exams.

Q: Hookworm infestation is associated with which of the following findings?

Chandler's index. **Explanation:** **Chandler’s Index** is the correct answer as it is a standard epidemiological measure used to assess the severity of hookworm infestation (primarily *Ancylostoma duodenale* and *Necator americanus*) in a community. It is calculated by taking the average number of eggs per gram (EPG) of stool across a sampled population. An index of less than 2000-2500 is generally considered low, while higher values indicate a significant public health problem and a higher risk of iron-deficiency anemia among the population. **Analysis of Incorrect Options:** * **Metafren index:** This is a distractor and not a recognized clinical or epidemiological scoring system in parasitology. * **MELD score (Model for End-Stage Liver Disease):** This is a scoring system used to predict the 3-month mortality risk in patients with chronic liver disease and is primarily used for prioritizing patients for liver transplantation. * **Burrows in skin:** This is the classic clinical finding of **Scabies** (*Sarcoptes scabiei*), where the female mite tunnels into the stratum corneum. While hookworms cause "creeping eruption" (Cutaneous Larva Migrans), they do not form permanent burrows in the same manner as scabies. **High-Yield Clinical Pearls for NEET-PG:** * **Hookworm Anemia:** The primary morbidity is microcytic hypochromic anemia due to chronic blood loss (0.03–0.2 ml/day/worm). * **Ground Itch:** An allergic reaction at the site of larval entry (usually the feet). * **Loeffler’s Syndrome:** Transient pulmonary eosinophilia occurring during the larval migration phase through the lungs. * **Treatment:** Albendazole (400 mg single dose) is the drug of choice.

Q: Cluster testing is useful in detecting cases of which of the following?

Sexually transmitted infections. **Explanation:** **Cluster testing** (also known as contact tracing or partner notification) is a specialized epidemiological technique used to identify infected individuals by investigating the social and sexual networks of a known index case. **1. Why Sexually Transmitted Infections (STIs) is correct:** STIs do not occur randomly in a population; they tend to occur in "clusters" among individuals sharing common risk behaviors or sexual networks. In cluster testing, once a case is diagnosed, the investigator identifies and tests their sexual partners and social contacts (the cluster). This is the most effective way to break the chain of transmission for infections like Syphilis, Gonorrhea, and HIV, where asymptomatic carriers often unknowingly spread the disease. **2. Why other options are incorrect:** * **Measles:** This is a highly contagious respiratory infection spread via droplets. Control relies on **outbreak investigation** and mass immunization rather than tracing specific social clusters. * **Unimmunized/Immunized children (12-23 months):** To estimate immunization coverage, the WHO recommends the **30-cluster sampling technique**. This is a *sampling methodology* used for surveys to estimate prevalence/coverage in a community, which is distinct from "cluster testing" used for case-finding in infectious diseases. **High-Yield Pearls for NEET-PG:** * **Cluster Testing:** Best for STIs (Syphilis is the classic example). * **30-Cluster Sampling:** Used for EPI (Expanded Programme on Immunization) coverage surveys. It involves 30 clusters of 7 or 10 children each. * **Snowball Sampling:** A qualitative research method often used to reach "hidden populations" (e.g., IV drug users) which shares some conceptual similarities with cluster testing.

Q: What percentage of multidrug-resistant tuberculosis (MDR TB) cases are extensively drug-resistant tuberculosis (XDR TB) worldwide?

10%. ### Explanation **Correct Answer: B. 10%** **Understanding the Concept:** According to the World Health Organization (WHO) Global Tuberculosis Reports, approximately **10%** of all multidrug-resistant tuberculosis (MDR-TB) cases are estimated to be extensively drug-resistant (XDR-TB). * **MDR-TB** is defined as resistance to at least **Isoniazid (H) and Rifampicin (R)**, the two most potent first-line drugs. * **XDR-TB** (Revised WHO definition) is MDR-TB that is also resistant to any **fluoroquinolone** AND at least one additional Group A drug (such as **Bedaquiline or Linezolid**). The 10% figure represents a critical epidemiological threshold used to monitor the escalation of drug resistance globally. **Analysis of Incorrect Options:** * **Option A (5%):** This is an underestimate. While resistance patterns vary by region, the global average has consistently hovered around the 9-10% mark in recent surveillance data. * **Options C & D (20% and 25%):** These figures are significantly higher than the global average. While some "hotspots" (certain Eastern European or Central Asian countries) may report higher proportions, they do not represent the worldwide prevalence. **High-Yield NEET-PG Pearls:** * **Pre-XDR TB:** MDR-TB that is resistant to any fluoroquinolone (but not yet to Group A drugs). * **Primary vs. Acquired Resistance:** Most XDR-TB cases in high-burden countries are now due to **primary transmission** rather than poor treatment adherence alone. * **Treatment Duration:** Under the National TB Elimination Program (NTEP), the treatment for drug-resistant TB has shifted toward shorter, all-oral regimens (e.g., BPaLM regimen: Bedaquiline, Pretomanid, Linezolid, and Moxifloxacin). * **Diagnostic Gold Standard:** Cartridge Based Nucleic Acid Amplification Test (**CBNAAT/GeneXpert**) is the initial investigation of choice to detect Rifampicin resistance.

Q: Which of the following parasitic infections is characterized by a cyclodevelopmental stage?

Filaria. In vector-borne diseases, the relationship between the parasite and the vector is classified based on whether the parasite multiplies or undergoes structural changes within the host. **Explanation of the Correct Answer:** **Filaria (Option B)** is the classic example of **Cyclodevelopmental** transmission. In this stage, the parasite undergoes essential developmental changes (e.g., microfilariae maturing into L1, L2, and infective L3 larvae) within the mosquito vector, but there is **no multiplication** in numbers. One microfilaria ingested results in only one infective larva. **Analysis of Incorrect Options:** * **Malaria (Option A):** Exhibits **Cyclo-propagative** transmission. The *Plasmodium* parasite undergoes both developmental changes (gametocyte to sporozoite) and significant multiplication (sporogony) within the female Anopheles mosquito. * **Plague (Option C):** Exhibits **Propagative** transmission. The *Yersinia pestis* bacteria simply multiply within the gut of the rat flea without undergoing any cyclic changes or metamorphosis. * **Cholera (Option D):** This is a water-borne/fecal-oral disease, not a vector-borne parasitic infection. It does not involve biological transmission through an arthropod vector. **High-Yield Clinical Pearls for NEET-PG:** 1. **Propagative:** Multiplication only (e.g., Plague, Yellow Fever, Dengue). 2. **Cyclodevelopmental:** Development only; no multiplication (e.g., Filaria, Guinea worm). 3. **Cyclo-propagative:** Both development and multiplication (e.g., Malaria). 4. **Transovarial Transmission:** When the pathogen is passed to the next generation of vectors via eggs (e.g., Scrub typhus/Trombiculid mites, Kyasanur Forest Disease/Ticks).

Question 1

Mites are known to transmit which of the following diseases?

Accepted Answer

Scabies

Answer

Relapsing fever

Answer

Kyasanur Forest Disease (KFD)

Answer

Human babesiosis

Question 2

Hookworm infestation is associated with which of the following findings?

Accepted Answer

Chandler's index

Answer

Metafren index

Answer

MELD score

Answer

Burrows in skin

Question 3

What are the mechanisms by which cholera might be maintained during the intervals between peak cholera seasons?

Accepted Answer

Continuous transmission in man

Answer

Carrier status in animals

Answer

Carrier status in man

Answer

An environmental reservoir

Question 4

Cluster testing is useful in detecting cases of which of the following?

Accepted Answer

Sexually transmitted infections

Answer

Measles

Answer

Unimmunized children

Answer

Completely immunized children in the age group 12-23 months

Question 5

All of the following are true for Hepatitis B EXCEPT one?

Accepted Answer

Vertical transmission is more important than horizontal transmission.

Answer

Age of onset determines the prognosis.

Answer

The period of communicability lasts several months.

Answer

The virus can be found in the blood one month before the onset of jaundice.

Question 6

What is the method of choice for mass screening of tuberculosis?

Accepted Answer

Sputum smear examination by direct microscopy

Answer

Tuberculin test

Answer

Mass Miniature Radiography (MMR)

Answer

Sputum culture

Question 7

What percentage of multidrug-resistant tuberculosis (MDR TB) cases are extensively drug-resistant tuberculosis (XDR TB) worldwide?

Accepted Answer

10%

Answer

5%

Answer

20%

Answer

25%

Question 8

Which of the following conditions is known to be transmitted vertically?

Accepted Answer

Herpes simplex

Answer

Leprosy

Answer

Tetanus

Answer

Whooping cough

Question 9

Which of the following parasitic infections is characterized by a cyclodevelopmental stage?

Accepted Answer

Filaria

Answer

Malaria

Answer

Plague

Answer

Cholera

Question 10

Which of the following statements about hepatitis B is FALSE?

Accepted Answer

Vertical transmission is more important than horizontal transmission.

Answer

The communicable period lasts for months.

Answer

The virus can be found in the blood 1 month before jaundice appears.

Answer

The age of onset determines the prognosis.

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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